1. Field of the Invention
The present invention relates to a method of forming a pattern in semiconductor device manufacturing process, and more particularly to a method of forming a pattern having a step difference on an insulator, a semiconductor substrate, and a semiconductor multilayer film formed on the semiconductor substrate and the like, and to a method of manufacturing a microstructural semiconductor device such as a quantum wire laser and a mesoscopic device, where fabrication is performed on a compound semiconductor substrate, and then a compound semiconductor is allowed to crystal grow to manufacture a semiconductor device.
2. Description of the Related Art
Lithography technique is essential for forming a pattern of a semiconductor device, so that a lithography with a simple and better controllability has been required. With respect to the achievement of high integration and of high function, a method using electron beam, ion beam and the like by which a micropatterning can be performed is more effective than the lithography using an ordinary UV light. For example, a literature by A. Milgram et al., J. Vac. Sci. Technol. B3, 879 (1985) describes an example of a micropatterning using FIB (Focused Ion Beam).
Although that method allows a resist mask to be formed on a semiconductor substrate, an SOG film and an organic photoresist film have been formed by a process such as spin coat and baking which are difficult to use in the vacuum, so that such method has not been adapted to the achievement of a composite process, thus to an integrated vacuum process.
In patterning an oxide film and the like on a substrate, not limited to a mask for substrate etching, the above-mentioned resist mask must be formed. As with the above, this case also has not been adapted to an integrated vacuum process.
Thus, the unadaptability of the method to an integrated vacuum process has caused productivity to be reduced, and dust adhering and native oxide film development to occur in a pattern, thereby having caused the reliability of a device finally produced to be lowered.
The step difference pattern for semiconductor substrates and the like has been used for part of many semiconductor devices, so that a method of forming such pattern with a simple and better controllability has been required. For example, a literature by H. Morimoto et al., J. Vac. Sci. Technol. B5, 211 (1987) describes an example of a technique of forming a T-shaped step difference pattern on an organic polymer resist to produce a mushroom gate of GaAs MESFET.
In the method of forming the pattern having a step difference and a T-shaped section by the use of such organic polymer resist, the resist is not suitable for a vacuum process, so that there have been a problem with respect to process consistency, and also another problem with respect to productivity such that a complex process is required to reduce a damage at the time of ion beam exposure.
A literature by O. Wada, J. Electrochem. Soc., Solid-State Sci. Technol. 131, 2373 (1984) describes an example of a technique of forming a monolithic lens on an LED substrate side to improve a light coupling efficiency of LED and optical fiber.
In the method of forming the lens of LED by the use of such resist mask, inclined patterns having difference pattern sizes cannot be simultaneously formed, so that there have been a problem with respect to productivity, and also another problem with respect to process consistency because such resist mask is a material unsuitable for a vacuum process.
A microstructural semiconductor device has been tried to be applied to a high-performance semiconductor device including a quantum wire laser by the use of its quantum size effect and the like. A method of manufacturing a quantum wire laser is described, as an example, in a literature by M. Cao et al., Trans, IEICE, E73, 1. pp. 63-70 (January, 1990).
In the method of manufacturing the semiconductor device, PMMA resist and electron beam exposure used mainly for micropattern formation, as well as microfabrication technique combining wet etching hardly avoid a complexed manufacture process due to regrowth interface oxidation and impurity contamination, and a deteriorated device characteristics. Since the resist pattern has not a sufficient dry etching durability, there has been a limit of fabrication ability due to the use of wet etching.